Undisclosed father identity is prominent among South African children growing up without a biological father. Reasons for paternity non-disclosure are not well-understood. Findings from three focus group discussions with 30 mothers and guardians, aged 25 to 35, from Johannesburg, South Africa identified factors that hinder paternity disclosure to children. Disclosure of father identity was difficult when there was denial of paternity, when the mother got pregnant by a married man, and when the whereabouts of the father was unknown. Fear of betraying the trust of family members also prevented disclosure. Undisclosed paternity is strongly woven with larger-scale cultural, social, and economic factors. Findings support the need to strengthen family planning, address gender-based violence, and women's economic dependence on their male partners in order for paternity disclosure to be safe. Clinical implications are discussed.